1. Field of the Invention
The present invention relates to a lens-fitted photo film unit having plural photographic modes.
2. Description of the Related Art
A lens-fitted photo film unit preloaded with an unexposed photo film is widely known. A lens-fitted photo film unit, in which photographic modes are selectable according to the various photography conditions in a range from bright place such as outdoors to a dark place, is known. The kind of lens-fitted photo film unit is disclosed in JP-A 2003-344914 and is commercially available as “Night&Day (product name)” from the applicant.
The above lens-fitted photo film unit can work in three different modes, a daylight photography mode which has no flash emission, a night view synchro photography mode and a daylight synchro photography mode which have flash emission. The daylight photography mode is used for photography in a bright place such as outdoors. The night view synchro photography mode is used for photography of a dark subject such as a night view or for photography of a main subject such as a person with a background such as a night view or a dark room while photographing the background at a proper density. In the daylight photography mode and the daylight synchro photography mode, a small stop and a high shutter speed are selected. In the night view synchro photography mode, a large stop and a low shutter speed are selected.
JP-A 2003-344914 discloses the lens-fitted photo film unit using a photo film of ISO sensitivity 1600. In the daylight photography mode and the daylight synchro photography mode, the shutter speed is set at 1/100 sec. and the f-number is f/14. In the night view synchro photography mode, the shutter speed is set at 1/45 sec. and the f-number is f/5.6.
When the daylight photography mode or the daylight synchro photography mode is selected, the shutter speed is set at high by reducing rotary angle of a shutter blade by a shutter speed changeover mechanism. As to the f-number, a fixed stop plate which corresponds to a large stop is disposed in a photographic lens. The shutter speed changeover mechanism is used for inserting a stop plate, on which a small stop is formed, to cover the fixed stop plate when the daylight photography mode or the daylight synchro photography mode is selected.
The lens-fitted photo film unit “Night&Day (product name)” has the same structure as the lens-fitted photo film unit disclosed in JP-A 2003-344914, except that the shutter speed is set at 1/120 sec. in the daylight photography mode or daylight synchro photography mode, and the f-number is f/6.2 in the night view synchro photography mode.
JP-A 2000-352800 discloses a lens-fitted photo film unit which is suitable for various photographic conditions from a bright place to a dark place, by changing over the shutter speed and the transmission light amount of the photographic lens. In this lens-fitted photo film unit, an ND filter is inserted in the photography optical path in cooperation with turning off of the flash switch, to reduce the exposure amount. Moreover, in a manner similar to the lens-fitted photo film unit disclosed in JP-A 2000-344914, the shutter speed is set at high by reducing rotary angle of the shutter blade.
However, there are problems in JP-A 2003-344914 and JP-A 2000-352800 that the shutter speed changeover mechanism is likely to operate at undesirable shutter speed due to unstable movement of the shutter blade. In addition, there are problems that the manufacturing cost is increased due to the increase in number of parts for changing over shutter speed, and that the size of the lens-fitted photo film unit is enlarged.
Incidentally, maximum brightness of photographing scene is generally considered to be the exposure value (EV) 16 with the photo film of ISO sensitivity 100. The photographing scene in the range of EV15 to EV16 is approximately 1% among the all photographing opportunities. It is noted that the proper EV using the photo film of ISO sensitivity 100 is obtained with substitution of the f-number “f”, the shutter speed “T”, and the film sensitivity “S” by the following equation:EV=log2(f2/T)−log2(S/100)For example, brightness of EV16 means proper brightness in the photography taken with the f-number, the shutter speed and the film sensitivity to meet EV16.
For example, when proper EV is set at EV10 about 1% among the all photographing opportunities in the daylight photography of the lens-fitted photo film unit, there causes overexposure beyond the latitude of the photo film, even allowing overexposure of +5 considering the latitude of the color negative film. Moreover, problems arise in that the whole image of the printed photo made from the overexposed frame becomes pinkish, and the developing cost is increased due to the prolonged printing time.
When proper EV is set at EV12 in the daylight photography of the lens-fitted photo film unit, lower limit within the latitude on the underexposure side is EV10. However, it is known that there are few users who recognize the brightness of EV10 to EV9 to be dark. Therefore, there is no problem caused from such overexposure as described above when the proper EV in the daylight photography is set at EV12. Even though the lens-fitted photo film unit is designed to have night view synchro photography mode which permits the brightness of EV10 to EV9, most of the users photograph in daylight photography mode, without shifting to the night view synchro photography mode. As a result, a proper photo print cannot be obtained.
Besides, the photography of a night view or a person with a night view background would be appropriately photographed under the proper EV values of equal to or less than EV6 with the photo film of ISO sensitivity 100. As described above, the inventors have found out that the proper EV in daylight photography is set in the vicinity of EV11, and the proper EV in night view photography is EV6.
In the lens-fitted photo film unit, in order to set the proper EV at 11 in daylight photography and at 6 in night view photography only by an aperture changeover mechanism, the combination of the shutter speed of 1/128 sec. (officially 1/120 sec.), f/2.8 in daylight photography and f/16 in night view photography, and the photo film of ISO sensitivity 1600 is considered. However, f/2.8 is not practical for the lens-fitted photo film unit which is manufactured at low cost, and constituted of one or two plastic taking lenses.
When the photo film of ISO sensitivity 3200 is used and the shutter speed is set at 1/64 sec. (officially 1/60 sec.) to overcome/deal with the camera shake, the f-number in night view photography can be f/5.6 which is practical level. However, in this case, f-number in daylight photography mode is f/32. Problems arise in that image quality is generally decreased due to diffraction of light at the stop when the f-number is more than f/22.